The present invention relates to the field of photography and, more particularly, to a camera including an automatic lens focusing system.
Commonly-assigned U.S. Pat. No. 4,167,316 and copending applications U.S. Ser. Nos. 017,196, and 017,425, now U.S. Pat. No. 4,243,309, both filed on Mar. 5, 1979, and U.S. Ser. No. 156,044, filed on June 3, 1980, disclose cameras of the type including an automatic lens focusing system that is formed in party by a sonic ranging system for measuring the photographic subject-to-camera distance.
Typically, the lens focusing system includes a plurality of discrete lens elements, each having a different focal length, mounted in circumferentially spaced apart relation on a lens holding disc for rotation about a disc center axis to sequentially present the lens elements at a focusing position for focusing image forming light rays emanating from a subject located within a corresponding subject-to-camera distance range at the camera's film plane.
As the sonic ranging system (which may be of the type described in commonly-assigned U.S. Pat. No. 4,199,246) operates, the disc is accelerated by the arm of a torsion spring or the end of a pivoting actuator member to impart rotary motion thereto. After receipt of an echo signal from the subject indicative of subject distance, a disc pawl operates to engage a corresponding one of a plurality of notches or tabs disposed about the periphery of the disc to thereby stop disc motion and locate the lens element corresponding to the indicated distance range at the focusing position.
Those skilled in the photographic art will appreciate that a lapsed time period from the beinning to the end of the automatic lens focusing portion of the camera cycle is relatively short. Typically, with a lens disc having four separate lens elements thereon, the lens pawl stops the disc to locate the first element at the focusing position within approximately 25 milliseconds after cycle initiation. The elapsed time for stopping the last of the four lens elements at the focusing position is approximately 80 milliseconds.
To insure that such rapid operation is performed reliably on a consistent basis, it is essential for the lens drive system to quickly and smoothly accelerate the lens disc to a substantially constant rotational velocity and for the disc or lens pawl to interact dynamically with the disc and the notches therein in a consistent and reliable manner to stop the disc by dissipating its inertial energy in such a way as to minimize disc oscillation and also to stabilize the position of the disc at each of its four focusing locations to accurately align the corresponding one of the lens elements with an exposure opening leading to the film plane.
In the previously-noted U.S. Pat. No. 4,167,316 the disc is provided with a series of tabs on the peripheral section extending outwardly in a direction transverse to the plane of rotation of the disc and the lens pawl includes a stop thereon which moves into the locus of travel of the tabs on stop disc rotation at the appropriate time. After engagement of the stop with one of the tabs, a torsion spring rotates the disc in the opposite direction so that the stop then becomes engaged with the tab associated with the next adjacent lens to locate it at the focusing position. The very nature of this action necessarily includes some disc bounce and oscillation which may lead to undesirable variation in the actual stopping time of the lens disc in each of its four focusing positions.
In the previously-noted copending applications, the disc is provided with notches having a shape that is generally complementary to the shape of the tang on the lens pawl. Initially, the pawl is in a retracted position so that the tang is outside of the locus of travel of the disc peripheral edge. In response to the echo signal indication, the lens pawl is pivoted toward the disc so that the tang rides along the edge of the disc in between adjacent notches until its leading edge engages a corresponding angled camming surface on the notch whereby it is cammed down into the notch to stop disc rotation. It will be noted that the peripheral edge in between adjacent notches radiates inwardly toward the notch to promote radially inward movement of the tang in preparation for its receipt into the approaching notch. However, such movement of the lens pawl caused by the changing radius of the peripheral edge may lead to a certain amount of instability in the lens pawl which could adversely effect the movement of the tang into the notch. Also, the complementary camming surfaces along the sides of the notch and tang have to be critically aligned so as not to bind, therefore making the piece parts more complex and expensive than is necessary.
Therefore, it is a primary object of the invention to provide a camera which includes such an automatic lens focusing position wherein the peripheral section of the disc including the notches and the tang on the lens pawl are configured to facilitate smooth cooperative operation to stop rotation of the lens disc in a more consistent and reliable manner.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.